In the liquefaction of condensible, normally gaseous materials, such as natural gas and air, which exist in the liquid form only at extremely low temperatures, it is common practice to pretreat the gas before liquefaction to remove therefrom any gaseous constituents which, at the low temperature of the liquefied gas, would exist in the solid form and would therefore create operating problems during the liquefaction process as well as in subsequent use of the liquefied material. Natural gas, which consists principally of methane, usually includes minor proportions of water vapor, carbon dioxide and heavier hydrocarbons, all of which freeze at temperatures above that which is required to liquefy the gas. Similarly, air usually contains minor proportions of carbon dioxide and water vapor which must be removed prior to liquefaction.
It is known to remove such constituents, herein referred to as "high boiling constituents", prior to liquefaction of the gas by adsorbing them on solid adsorbents, such as zeolites, in a preliminary step before the gas is fed to the liquefaction plant. Such solid adsorbents, however, eventually become exhausted in their ability to adsorb any additional material and must be regenerated for reuse by removal of the adsorbed materials. It has been proposed to regenerate the exhausted or spent adsorbents by subjecting them to a sufficiently low pressure to cause the desorption of the adsorbed materials therefrom, thus regenerating their adsorptive capacity. The methods heretofore contemplated or proposed for this purpose employed mechanical pumps, which in the large sizes necessary for treating such materials on an industrial scale were incapable of reaching a pressure sufficiently low for substantially complete regeneration of the adsorbent. Although the pressures which could be reached with mechanical vacuum pumps were sufficiently low to cause the desorption of carbon dioxide and hydrocarbons heavier than methane from the solid adsorbent, they were too high to remove water, so that the regeneration of the adsorbent was not complete.